KR102579103B1 - How to electrically connect contact surfaces of electronic components - Google Patents

Abstract

The present invention provides a method for electrically connecting a contact surface of a first electronic component with a contact surface of a second electronic component, comprising: (1) connecting a wire having a circular cross-section with an average diameter of 8 to 80 μm to the contact surface of the first electronic component; bonding the capillary wedge to the contact surface; (2) lifting the capillary wedge bonded wire to form a wire loop between the capillary wedge bond formed in step (1) and the contact surface of the second electronic component; and (3) stitch bonding the wire to a contact surface of the second electronic component, the wire comprising a wire core having a surface, the wire core having a double layer coating superimposed on the surface, the wire core It is composed of a material selected from the group consisting of pure silver, doped silver with a silver content of more than 99.5 wt% and silver alloys with a silver content of more than 89 wt%, said double layer coating comprising nickel or palladium inside with a thickness of 1 to 50 nm. layer and an adjacent gold outer layer having a thickness of 5 to 200 nm.

Description

How to electrically connect contact surfaces of electronic components

The present invention relates to a method of electrically connecting contact surfaces of electronic components using a coated wire comprising a silver or silver-based core and a double layer coating superimposed on the surface of the core.

Wire bonding techniques are well known to those skilled in the art. In the wire bonding process, a first bond is formed on the contact surface of the first electronic component and a second bond is formed on the contact surface of the second electronic component. The two bonds are the terminals of the connecting bonding wire segments between them.

The term “electronic component” is used herein. As used herein, the term “electronic component” includes in the context substrates and semiconductors used in the electronic or microelectronic field. Examples of substrates include lead frames, ball grid arrays (BGAs), printed circuit boards (PCBs), flexible electronics, glass substrates, ceramic substrates such as direct aluminum bonding (DAB) or direct copper bonding (DCB) substrates, and IMS. (insulated metal substrate). Examples of semiconductors include diodes, LEDs (light emitting diodes), dies, IGBTs (insulated gate bipolar transistors), ICs (integrated circuits), MOSFETs (metal oxide semiconductor field effect transistors), and sensors.

The term “contact surface” is used herein. It refers to the electrical contact surface of an electronic component to which bonding wires can be connected through wire bonding. Typical examples are bond pads of semiconductors and contact surfaces of substrates (e.g. plated fingers, plated grounds). The bond pad may be comprised of a metal or metal alloy or may have a thin (eg, 0.5 to 1 μm) top layer comprised of a specific metal or metal alloy. The bond pad may have a surface made of, for example, aluminum, copper, nickel, silver, gold or an alloy based on one of these metals. The overall thickness of the bond pad may be, for example, 0.6 to 4 μm, and the area may be, for example, 20 μm×20 μm to 300 μm×300 μm, preferably 35 μm×35 μm to 125 μm×125 μm. .

The use of bonding wires in electronics and microelectronics applications is a well-known, state-of-the-art technology. Bonding wires were initially made of gold, but today cheaper materials such as copper, copper alloys, silver and silver alloys are used. These wires may have a metallic coating.

Regarding the geometry of the wire, the most common are bonding wires of circular cross-section.

A common fine wire bonding technique well known to those skilled in the art is ball-wedge wire bonding (abbreviated as "ball-wedge bonding"), which consists of a ball bond (primary bond) and a stitch bond (secondary bond). bond, wedge bond) is formed.

Recently, a fine wire bonding technology has been reported in which the primary ball bonding step is replaced by a so-called capillary wedge bonding step (e.g., Sarangapani Murali et al.'s paper "Aluminum Wedge-Wedge Bonding Using Capillary and Ball Bonder " IMAPS 2017 - ^50th International Symposium on Microelectronics - Raleigh NC USA, Oct. 9-12, 2017). This type of fine wire bonding process is distinguished by the formation of capillary wedge bonds (primary wedge bonds) and conventional stitch bonds (secondary wedge bonds).

Capillary wedge bonding omits forming a wire ball or FAB (free air ball) at the wire tip as in conventional ball bonding. Capillary wedge bonding offers improved productivity compared to ball bonding, especially with regard to so-called cascade wire bonding (often referred to as cascade wire bonding (wire bonding in stacked die applications)).

US 2015/0187729 A1 discloses capillary wedge bonding of gold wires, copper wires and aluminum wires.

WO 2017/091144 A1 discloses a bonding wire comprising a silver or silver-based wire core with a coating layer superimposed on the surface, wherein the coating layer is a single layer of gold or palladium from 1 to 1000 nm, or from 1 to 100 nm, It is preferably a double layer consisting of an inner layer of nickel or palladium, 1 to 20 nm thick, and an adjacent outer layer of gold, 1 to 200 nm thick, preferably 1 to 40 nm thick.

Applicants have discovered that certain types of coated silver wire or coated silver-based wire are unexpectedly suitable for use as bonding wires in primary capillary wedge/secondary stitch wire bonding applications with a focus on the primary capillary wedge wire bonding step. ; That is, it has been found that when performed using this particular type of coated silver wire or coated silver-based wire, the primary capillary wedge wire bonding step is distinguished by an unexpectedly wide capillary wedge bonding process window.

Like other wire bonding processes, capillary wedge bonding exhibits a so-called process window. This capillary bonding process window is described further below.

The specific type of coated silver wire or coated silver-based wire mentioned above includes a wire core with a surface, the wire core having a double-layer coating superimposed on the surface, and the wire core itself is pure silver, with a silver content of 99.5 wt%. Consisting of excess doped silver and a silver alloy with a silver content of at least 89 wt%, the double layer coating consists of an inner layer of nickel or palladium from 1 to 50 nm thick and an adjacent outer layer of gold from 5 to 200 nm thick.

Accordingly, the present invention relates to a method for electrically connecting a contact surface of a first electronic component with a contact surface of a second electronic component, the method comprising:

(1) capillary wedge bonding a wire of circular cross-section with an average diameter of 8 to 80 ㎛ to the contact surface of the first electronic component;

(2) lifting the capillary wedge bonded wire to form a wire loop between the capillary wedge bond formed in step (1) and the contact surface of the second electronic component; and

(3) stitch bonding the wire to the contact surface of the second electronic component

Includes,

The capillary wedge bonding in step (1) is performed using a ceramic capillary with a lower face angle in the range of 0 to 4 degrees,

The wire includes a wire core having a surface, the wire core having a double layer coating superimposed on the surface,

The wire core itself is comprised of a material selected from the group consisting of pure silver, doped silver with a silver content greater than 99.5 wt% and silver alloys with a silver content greater than 89 wt%,

The double layer coating consists of an inner layer of nickel or palladium from 1 to 50 nm thick and an adjacent outer layer of gold from 5 to 200 nm thick.

In step (1) of the method of the present invention, a wire is capillary wedge bonded to a contact surface of a first electronic component. In this step (1), a ceramic capillary with a bottom angle in the range of 0 to 4 degrees is used as a bonding tool.

The ceramic capillary supplies ultrasonic energy and compressive force. Examples of ceramic capillaries include alumina or zirconia doped alumina capillaries.

Capillary wedge bonding in step (1) uses a KNS bonder such as the KNS-iConn bonder (Kulicke & Soffa Industries Inc., Port Washington, PA, USA), or a Shinkawa bonder such as the Shinkawa-UTC-5000, NeoCu bonder from Japan. It can be performed by doing this.

The capillary wedge bonding process parameters of step (1) include at least one, preferably two or more, and most preferably all of (a) to (i) below.

(a) ultrasonic energy in the range of 50 to 100 mA,

(b) force ranging from 10 to 30 g (compressive force),

(c) constant speed in the range of 0.3 to 0.3 μm/s; Constant speed refers to the speed at which the wire contacts the bond pad.

(d) contact threshold ranging from 60 to 70%; Contact threshold detects contact with the bond pad or contact surface, measured as the percentage drop in contact speed (in KNS terms, i.e. when using KNS-iConn bonders) or seeking speed (in Shinkawa terms, i.e. when using Shinkawa bonders). It is a parameter that controls the sensitivity of the bond head in

(e) bonding temperature ranging from 25 to 175 °C,

(f) cut tail length in the range of 85 to 110 μm (Shinkawa terminology, i.e. when using Shinkawa bonders);

(g) cut length extension in the range of 200 to 500 μm (KNS terminology, i.e. when using Shinkawa bonders);

(h) sink amount in the range of -6 to -12 μm (when using Shinkawa terminology, i.e. Shinkawa bonder); The sinking amount is a process parameter that controls the mechanical deformation of the wire induced by ultrasonic energy and compression force through the capillary tip; Wire strain is the downward strain relative to the wire surface, measured in μm and expressed as a negative value;

(i) Ultrasonic ramp (in KNS terms, i.e. when using KNS-iConn bonders) or ultrasonic ramp (in Shinkawa terms, i.e. when using Shinkawa bonders) ranging from 0 to 50%.

In other words, when step (1) is performed using a KNS-iConn bonder, the capillary wedge bonding process parameters of step (1) are at least one, preferably two or more of (a') to (g') below, Most preferably it includes all:

(a') ultrasonic energy ranging from 50 to 100 mA,

(b') force ranging from 10 to 30 g,

(c') constant velocity in the range of 0.3 to 0.7 μm/s,

(d') contact threshold ranging from 60 to 70%,

(e') a bonding temperature ranging from 25 to 175° C.,

(f') an extension of the tail length ranging from 200 to 500 μm, and

(g') Ultrasonic lamp ranging from 0 to 50%.

On the other hand, when step (1) is performed using a Shinkawa bonder, the capillary wedge bonding process parameters of step (1) are at least one, preferably two or more of the following (a") to (g"), and most preferably: includes all:

(a") ultrasonic energy in the range of 50 to 100 mA,

(b") force ranging from 10 to 30 g,

(c") constant velocity in the range of 0.3 to 0.7 μm/s,

(d") contact threshold ranging from 60 to 70%;

(e") bonding temperature ranging from 25 to 175° C.,

(f") cut tail length ranging from 85 to 110 μm,

(g") a sink amount ranging from -6 to -12 μm, and

(h") Ultrasonic slope ranging from 0 to 50%.

The capillary wedge bonding in step (1) represents the so-called capillary wedge process window, which can be described in several approaches, three of which are described below.

In the first approach, capillary wedge bond formation is considered to involve the application of a specific compressive force (typically measured in grams) supported by the application of ultrasonic energy (typically measured in mA). The mathematical product of the difference between the upper and lower limits of the applied force and the upper and lower limits of the applied ultrasonic energy in the capillary wedge bonding process can herein define the capillary wedge bonding process window.

(Upper limit of applied force - Lower limit of applied force)·(Upper limit of applied ultrasonic energy - Lower limit of applied ultrasonic energy) = Capillary wedge bonding process window.

In the second approach, capillary wedge bond formation is considered to involve the application of a specific force (usually measured in grams) supported by a sinking quantity. The mathematical product of the difference between the upper and lower limits of the applied force and the upper and lower limits of the sink amount in the capillary wedge bonding process can herein define the capillary wedge bonding process window.

(Upper limit of applied force - Lower limit of applied force) · (Absolute value of upper limit of sink amount - Absolute value of lower limit of sink amount) = Capillary wedge bonding process window.

In the third approach, capillary wedge bond formation is considered to involve the application of a specific force (usually measured in grams) supported by a scrub amplitude. Scrub amplitude is a process parameter that controls the mechanical motion of the capillary tip (circular, vertical, in-line (along the wire axis)) and consequently transforms the wire into horseshoe-shaped thin wire sections. Scrub amplitude is typically measured in μm. The mathematical product of the difference between the upper and lower limits of the applied force and the upper and lower limits of the scrub amplitude in the capillary wedge bonding process can herein define the capillary wedge bonding process window.

(Upper limit of applied force - Lower limit of applied force) · (Upper limit of scrub amplitude - Lower limit of scrub amplitude) = Capillary wedge bonding process window.

Therefore, the capillary wedge bonding process window is the force/ultrasonic energy combination area, the force/sink quantity combination area, or the force/ultrasonic energy combination area, or /Defines the scrub amplitude combination area.

For industrial applications, the robustness of the capillary wedge bonding process allows for a wide capillary wedge bonding process window (force in g vs. ultrasonic energy in mA, force in g vs. sink amount in µm, or force in g vs. scrub in µm). It is desirable to have an amplitude). The method of the invention, or more precisely step (1) of the method of the invention, is distinguished by an unexpectedly wide capillary wedge bonding process window. Wire coating appears to be the key to an unexpectedly wide capillary wedge bonding process window.

The wire used in the method of the present invention is a round bonding wire for bonding in microelectronics. The wire is preferably an integrated entity. The average diameter ranges from 8 to 80 μm, preferably from 12 to 55 μm or 17 to 50 μm.

The average diameter or simply the diameter of the wire or wire core can be obtained by the “sizing method”. According to this method, the physical weight of the wire for a defined length is determined. Based on this weight, calculate the diameter of the wire or wire core using the density of the wire material. The diameter is calculated as the arithmetic mean of five measurements for five cuts of a particular wire.

The wire includes a wire core with a surface, the wire core having a double layer coating overlaid on the surface, the wire core itself being made of pure silver, doped silver with a silver content greater than 99.5 wt% and silver with a silver content greater than 89 wt%. Composed of an alloy, the double-layer coating consists of an inner layer of nickel or palladium from 1 to 50 nm thick and an adjacent outer layer of gold from 5 to 200 nm thick. For brevity, this coated wire is sometimes abbreviated as “wire” herein.

The term “pure silver” is used herein. It means silver with a purity of 99.95 to 100 wt%. It may contain up to 500 wtppm (ppm by weight) of additional components (non-silver) in total.

The term “doped silver” is used herein. It refers to a type of silver consisting of silver in an amount ranging from greater than 99.5 to 99.997 wt% and at least one doping element in a total amount of up to less than 5000 wtppm (eg, from 30 to less than 5000 wtppm). It may contain up to 500 wtppm of additional components (components other than silver and at least one doping element) in total amounts.

The term “silver alloy” is used herein. It is an alloy consisting of silver in the range of 89 to 99.50 wt% and at least one alloying element in a total amount of 0.50 to 11 wt%, preferably of silver in the range of 92 to 99.50 wt% and at least one alloy element in a total amount of 0.50 to 8 wt%. alloying elements, or even alloys consisting of silver in the range of 96 to 99.50 wt% and at least one alloying element in a total amount of 0.50 to 4 wt%. It may comprise less than 5000 wtppm in maximum total amount (eg, less than 30 to less than 5000 wtppm) of at least one doping element (excluding at least one alloying element). It may contain up to 500 wtppm of additional components (elements other than silver, at least one alloying element and at least one doping element) in a total amount of up to 500 wtppm.

Examples of preferred alloying elements include palladium, gold, nickel, platinum, copper, rhodium and ruthenium.

Examples of preferred doping elements include calcium, nickel, platinum, copper, rhodium and ruthenium.

As already mentioned, the core of the wire may contain a total amount of up to 500 wtppm of so-called additional components. Additional components, often referred to as “unavoidable impurities,” are impurities present in the raw materials used or small amounts of chemical elements and/or compounds resulting from the wire manufacturing process. The low total amount of additional components from 0 to 500 wtppm ensures good reproducibility of wire properties. Additional ingredients present in the core are usually not added separately. Each individual additional component may be included in an amount of less than 30 wtppm, preferably less than 15 wtppm, based on the total weight of the wire core.

As previously mentioned, the wire core is comprised of pure silver, doped silver, or silver alloy.

The core of the wire is a homogeneous region of bulk material. Since bulk materials always have surface areas that may exhibit somewhat different properties, the properties of the core of a wire are understood as properties of homogeneous regions of the bulk material. The surfaces of bulk material regions may differ in morphology, composition (eg, sulfur, chlorine, and/or oxygen content), and other characteristics. The surface is the interface area between the wire core and the double layer of coating superimposed on the wire core. Typically, the double layer of coating completely overlaps the surface of the wire core. In the wire area between the core and the overlying double layer coating, a material combination of both the core and the double layer coating may be present.

A double-layer coating superimposed on the surface of the wire consists of an inner layer of nickel or palladium 1 to 50 nm thick, preferably 1 to 20 nm thick, and an adjacent outer gold layer 5 to 200 nm thick, preferably 10 to 100 nm thick. It is composed. In this context, “thickness” or “coating layer thickness” means the dimension of the coating layer in the direction perpendicular to the longitudinal axis of the core.

With regard to the composition of the double layer coating, the nickel or palladium content of the inner layer is, for example, at least 50 wt%, preferably at least 95 wt%, based on the total weight of the inner coating layer. A particularly preferred inner coating layer consists of pure nickel or palladium. Pure nickel or palladium typically contains less than 1 wt% of additional components (components other than nickel or palladium) based on the total weight of the inner coating layer. The gold content of the adjacent outer gold layer is, for example, at least 50 wt%, preferably at least 95 wt%, based on the total weight of the outer coating layer. A particularly preferred outer coating layer consists of pure gold. Pure gold typically contains less than 1 wt% of additional components (non-gold components) based on the total weight of the outer coating layer.

In one embodiment, the wire is characterized by at least one of the following external properties (α) to (θ):

(α) The corrosion resistance has a capillary wedge lift value of 5% or less (e.g., in the range of 0 to 5%, preferably in the range of 0 to 0.1%) (see “Test Method A” described below).

(β) The moisture resistance has a capillary wedge lift value (see “Test Method B” described below) of 5% or less (e.g., in the range of 0 to 5%, preferably in the range of 0 to 0.1%).

(γ) The resistivity of the wire is less than 4.0 μΩ·cm (e.g., in the range of 1.6 to 4.0 μΩ·cm, preferably in the range of 1.63 to 3.4 μΩ·cm) (see “Test Method C” described below).

(δ) The dendritic growth of silver in the wire is less than or equal to 12 μm/s (e.g. in the range of 0 to 12 μm/s, preferably in the range of 0 to 2 μm/s) (see “Test Method D” described below).

(ε) The hardness of the wire core is 80 HV (10 mN/12 s) or less (e.g. in the range of 50 to 80 HV, preferably in the range of 50 to 70 HV) (see “Test Method E” described below).

(ζ) The process window area for primary capillary wedge bonding is at least 200 mA·g (e.g., 400 to 600 mA for a 17.5 μm diameter wire capillary wedge bonded to a Cu bond pad of 0.5 wt% Al). ·g) (see “Test Method F” described later).

(η) The process window area for secondary stitch bonding (secondary wedge) is at least 50 mA·g (e.g., 125 to 175 mA·g for a wire stitch with a diameter of 17.5 μm bonded to a gold finger) (as described below) It has the value of “Test Method G”).

(θ) The yield strength of the wire is 170 MPa or less (e.g., in the range of 140 to 170 MPa) (see “Test Method H” described below).

The term “external properties” is used herein in relation to the wire core. While extrinsic properties depend on the relationship of the wire core with other factors such as the measurement method and/or measurement conditions used, intrinsic properties refer to the properties that the wire core has on its own (independent of other factors).

The wire used in the method of the present invention has the unexpected advantage of allowing capillary wedge bonding with a significantly wider capillary wedge bonding process window. The wire may be manufactured by a method comprising at least steps (i) to (v).

(i) providing a precursor item comprised of pure silver, doped silver, or a silver alloy,

(ii) forming a stretched precursor item by stretching the precursor item until a median cross-section in the range of 7850 to 49000 μm ² or a median diameter in the range of 100 to 250 μm, preferably 130 to 140 μm, is obtained,

(iii) depositing a coating of a double layer of a nickel or palladium inner layer (base layer) and an adjacent gold outer layer (top layer) on the surface of the drawn precursor item obtained after completion of process step (ii),

(iv) further stretching the coated precursor item obtained after completion of process step (iii) until the desired final cross-section or diameter is obtained, and

(v) Finally, strand annealing the coated precursor obtained after completion of process step (iv) at an oven setting temperature ranging from 200 to 600° C. for an exposure time ranging from 0.4 to 0.8 seconds to form a wire.

The term “strand annealing” is used herein. It is a continuous process that can produce wire quickly with high reproducibility. In the context of the present invention, strand annealing means that the annealing is carried out dynamically while the coated precursor to be annealed is pulled or moved through a conventional annealing oven and, after leaving the annealing oven, is wound onto a reel. Here, the annealing oven is typically in the form of a cylindrical tube of predetermined length. For example, annealing time/oven temperature parameters can be defined and set using a defined temperature profile at a given annealing rate that can be selected in the range of 10 to 60 m/min.

Herein, the term “oven set temperature” is used. It refers to the fixed temperature in the temperature controller of the annealing oven.

The present disclosure distinguishes between precursor items, drawn precursor items, coated precursor items, coated precursors, and coated wires. The term "precursor item" is used for wire pre-stages that have not reached the desired final cross-section or final diameter of the wire core, while the term "precursor" refers to wire at the desired final cross-section or desired final diameter. Used in the previous step. After completion of process step (v), i.e. annealing the final strand of the coated precursor to the desired final cross-section or desired final diameter, a wire that can be used in the process of the invention is obtained.

The precursor item provided in process step (i) may consist of sterling silver. Typically, these precursor items are in the form of rods with a diameter of, for example, 2 to 25 mm and a length of, for example, 2 to 100 m. These silver bars can be made by continuously casting silver using an appropriate mold, followed by cooling and solidification.

Alternatively, the precursor item provided in process step (i) may consist of doped silver or silver alloy. These precursor items can be obtained by alloying, doping, or alloying and doping silver with desired amounts of the required components. Doped silver or silver alloys can be prepared by conventional processes known to those skilled in the art of metal alloys, for example by melting the components together in the desired proportional proportions. In doing so, one or more existing parent alloys can be used. The melting process can be carried out, for example, using an induction furnace, and it is convenient to work under vacuum or under an inert gas atmosphere. The resulting melt can be cooled to form homogeneous pieces of the silver-based precursor item. Typically, these precursor items are in the form of rods with a diameter of, for example, 2 to 25 mm and a length of, for example, 2 to 100 m. These bars can be made by continuously casting the doped silver or (doped) silver alloy melt using a suitable mold, followed by cooling and solidification.

In process step (ii), the precursor item is stretched until a median cross-section in the range of 7850 to 49000 μm ² or a median diameter in the range of 100 to 250 μm, preferably 130 to 140 μm, is obtained, forming a stretched precursor item. do. Techniques for stretching precursor items are known. Preferred techniques include rolling, swaging, die drawing, etc., with die drawing being particularly preferred. In the latter case, the precursor item is drawn in several process steps until the desired intermediate cross-section or desired intermediate diameter is reached. These wire die drawing processes are well known to those skilled in the art. Conventional tungsten carbide and diamond drawing dies can be used, and conventional drawing lubricants can be used to aid drawing.

Step (ii) may include one or more substeps of intermediate batch annealing of the stretched precursor item at an oven set temperature ranging from 400 to 800° C. for an exposure time ranging from 50 to 150 minutes. Intermediate batch annealing can be performed, for example, using rods drawn to a diameter of about 2 mm and wound on a drum.

The optional intermediate batch annealing of process step (ii) may be performed under an inert or reducing atmosphere. Many types of inert atmospheres, as well as reducing atmospheres, are known in the art and used to purge annealing ovens. Nitrogen or argon are preferred as known inert atmospheres. As a known reducing atmosphere, hydrogen is preferred. Another preferred reducing atmosphere is a mixture of hydrogen and nitrogen. A preferred mixture of hydrogen and nitrogen is 90 to 98 vol. % nitrogen and therefore 2 to 10 vol. % hydrogen, with a total of 100 vol. %. Preferred mixtures of nitrogen/hydrogen are 90/10, 93/7, 95/5 and 97/3 vol%/vol%, respectively, based on the total volume of the mixture.

In process step (iii), a double layer coating consisting of an inner layer of nickel or palladium and an adjacent outer layer of gold is deposited on the surface of the drawn precursor item obtained after completion of process step (ii), thereby forming the coating as described above. Superimpose on the surface.

A person skilled in the art knows how to calculate the thickness of this coating on the drawn precursor item in order to finally obtain a coating of the layer thickness disclosed for the embodiment of the wire, i.e. after the coated precursor item has been finally stretched. Those skilled in the art are aware of many techniques for forming a coating layer of a material according to an embodiment on a silver or silver alloy surface. Preferred techniques are plating, such as electroplating and electroless plating, deposition of materials from a vapor phase, such as sputtering, ion plating, vacuum deposition and physical vapor deposition, and deposition of materials from a melt. Electroplating is the preferred technique.

In process step (iv), the coated precursor item obtained after completion of process step (iii) is further stretched until the desired final cross-section or diameter of the wire is obtained. The technique for stretching the coated precursor item is the same stretching technique as mentioned in the above disclosure of process step (ii).

In process step (v), the coated precursor obtained after completion of process step (iv) is finally subjected to an exposure time ranging from 0.4 to 0.8 seconds at an oven set temperature ranging from 200 to 600° C., preferably from 200 to 400° C. The strand is annealed to form the coated wire.

In a preferred embodiment, the final strand annealed coated precursor, i.e. still hot coated wire, is quenched in water which may contain one or more additives, for example 0.01 to 0.07% by volume of the additive(s). Quenching in water means cooling the final strand annealed coated precursor immediately or rapidly, i.e. within 0.2 to 0.6 seconds, from the temperature experienced in process step (v) to room temperature, for example by immersion or dropping.

After completing process step (v) and optional quenching, the coated wire is complete. In order to take full advantage of its properties, it is appropriate to use it without delay in wire bonding applications immediately, for example within 28 days after completion of process step (v).

In step (2) of the method of the present invention, the capillary wedge bonded wire is lifted to form a wire loop between the capillary wedge bond formed in step (1) and the contact surface of the second electronic component. The formation of the bonding wire loop with the desired loop shape and the desired loop process profile (capillary motion) is carried out in a conventional manner known to those skilled in the art and therefore does not require detailed description. It can be worked out according to the procedures described in the KNS Process User Guide for looping profiles (Kulicke & Soffa Industries Inc., Port Washington, PA, USA, 2002). Loop shape and loop processing profile can be determined by adjusting looping parameters (e.g., twist height, reverse operation, twist distance, twist angle, loop coefficient, shape angle, span length, final twist angle, and/or final twist length). Examples of loop process profiles include standard loop, machined loop, BGA2-loop, BGA3-loop, BGA4-loop, BGA5-loop, K-loop, PSA-loop, and ULL-loop.

In step (3) of the method of the present invention, the bonding wire is stitch bonded to the contact surface of the second electronic component. This stitch bonding procedure of step (3) is well known to those skilled in the art and does not include methodological features. Common stitch bonding equipment or stitch bonding tools can be used. It can be worked according to the procedures described in the KNS Process User's Guide to stand-off stitch bond (SSB) (Kulicke & Soffa Industries Inc., Port Washington, PA, USA, 2003). Stitch bonding process parameters include, for example, a bonding force in the range of 5 to 500 g, an ultrasonic energy, for example, in the range of 5 to 200 mA, a temperature, for example, in the range of 25 to 250° C., and a constant speed, for example, in the range of 2.5 to 40 μm/ms, for example 3 to 30 μm/ms. The bonding time may be in the ms range.

As already mentioned, steps (1) to (3) of the method of the present invention are subsequent steps. However, there may be one or more additional substeps, for example steps that occur before, between or after step sequences (1) to (3).

In an embodiment of the method of the present invention, the first electronic component is a semiconductor with a contact surface in the form of a substrate with a contact surface or a bond pad, and the second electronic component is a substrate with a contact surface or a contact in the form of a bond pad. It is a semiconductor with a surface. In a first modification of the above embodiment, the first electronic component is a semiconductor having a contact surface in the form of a bond pad, and the second electronic component is a substrate having a contact surface. In a second modification of the above embodiment, the first electronic component is a substrate with a contact surface, and the second electronic component is a semiconductor with a contact surface in the form of a bond pad.

yes

Test methods A to H

All tests and measurements were performed at T = 20°C and relative humidity RH = 50%.

A. Salt solution immersion test of capillary wedge bonds:

The wire was capillary wedge bonded to a Cu bond pad with 0.5 wt% Al. The test device with these bonded wires was immersed in a salt solution for 10 minutes at 25°C and then washed with deionized (DI) water and then with acetone. The salt solution contained 20 wtppm NaCl in DI water. The number of lifted wedge bonds was examined under a low power microscope (Nikon MM-40) at 100X magnification. Observation of a larger number of lifted capillary wedge bonds revealed severe interfacial galvanic corrosion.

B. Moisture resistance test of capillary wedge bond:

The wire was capillary wedge bonded to a Cu bond pad with 0.5 wt% Al. The test device with these bonded wires was stored in a highly accelerated stress test (HAST) chamber at a temperature of 130°C and 85% relative humidity (RH) for 8 hours and later analyzed at 100X magnification. The number of lifted wedge bonds was examined using a low-power microscope (Nikon MM-40). Observation of a larger number of lifted capillary wedge bonds revealed severe interfacial galvanic corrosion.

C. Electrical resistance:

Both ends of the specimen, that is, a wire with a length of 1.0 m, were connected to a power source providing a constant current/voltage. Resistance was recorded with a device for supply voltage. The measuring device was a HIOKI model 3280-10, and the test was repeated with at least 10 specimens. The arithmetic mean of the measurements was used in the calculations given below.

Resistance R was calculated according to R = V/I.

The resistivity ρ was calculated according to ρ = (R

Specific conductivity σ was calculated according to σ = 1/ρ.

D. Electron transfer test of wire:

Two wires of 75 μm diameter were held parallel within a distance of 1 mm on a glass plate under the objective lens of a low-power microscope model Nikon MM-40 with 50X magnification. A water droplet was formed using a micropipette between two wires to be electrically connected. One wire was connected to the anode and the other to the cathode, and +5 V was applied to these wires. Both wires were biased with +5 V direct current in a closed circuit in series with a 10 kΩ resistor. The circuit was closed by wetting the two wires with a few drops of deionized water as electrolyte. In the electrolyte forming silver dendrites, silver electrons moved from the cathode to the anode, sometimes bridging the two wires. The growth rate of silver dendrites is highly dependent on the coating layer of the wire and, in the case of silver alloy wire cores, the alloying additions.

E. Vickers micro hardness:

Hardness was measured using a Mitutoyo HM-200 test equipment equipped with a Vickers indenter. A force of 10 mN indentation load was applied to the specimen of wire for a dwell time of 12 seconds. The test was performed at the center of the wire or FAB.

F. Capillary wedge bonding (primary wedge) process window area:

Measurement of the capillary wedge bonding process window area was performed by standard procedures. The test wire was capillary wedge bonded to the Al 0.5 wt% Cu bond pad of the silicon die using a KNS-iConn bonder tool (Kulicke & Soffa Industries Inc., Port Washington, PA, USA). The important capillary wedge bonding process parameters were: ultrasonic energy of 75 mA, compression force of 20 g, constant speed of 0.5 μm/s, contact threshold of 65%, bonding temperature of 150°C, tail length extension of 350 μm, and 25% ultrasonic lamp. The process window value was based on a wire with an average diameter of 17.5 ㎛.

Four corners of the process window were derived by overcoming the following two main failure modes:

(1) Supplying too low a force and ultrasonic energy results in non-stick on pad (NSOP) of the wire, and

(2) Supplying too high a force and ultrasonic energy results in SHTL (short wire tail).

G. Stitch bonding (secondary wedge) process window area:

Measurement of the stitch bonding process window area was performed by standard procedures. Test wires were stitch bonded to gold-plated lead fingers on a ball grid array (BGA) substrate using a KNS-iConn bonder tool (Kulicke & Soffa Industries Inc., Port Washington, PA, USA). The process window value was based on a wire with an average diameter of 17.5 ㎛.

Four corners of the process window were derived by overcoming the following two main failure modes:

(1) Supplying too low a force and ultrasonic energy results in non-stick on lead finger (NSOL) of the wire, and

(2) Supplying too high a force and ultrasonic energy results in SHTL (short wire tail).

H. Elongation (EL)

The tensile properties of the wire were tested using an Instron-5564 instrument. The wire was tested at a speed of 2.54 cm/min over a 254 mm gauge length (L). Load to failure and elongation were obtained according to ASTM standard F219-96. Elongation is the difference (ΔL) in the gauge length of the wire between the beginning and end of the tensile test and is commonly reported as a percentage (100·ΔL/L) calculated from a plot of recorded load versus extensional tension. Tensile strength and yield strength were calculated by dividing the failure and yield load by the wire area. By weighing a standard length of wire and using its density, the actual diameter of the wire was determined by a sizing process.

Wire specimens 1 to 12

Silver (Ag), palladium (Pd) and gold (Au) of at least 99.99% purity (“4N”) in each case were melted in a crucible. A small amount of silver-nickel, silver-calcium, silver-platinum or silver-copper mother alloy was added to the melt and stirred to confirm uniform distribution of the added components. The following parent alloys were used.

For the alloys in Table 1, the corresponding parent alloy combinations were added.

Thereafter, wire core precursor items in the form of 8 mm rods were continuously cast from the melt. Afterwards, the rod was drawn in several drawing steps to form a wire core precursor with a circular cross-section of 134 μm in diameter. The wire core precursor was intermediate batch annealed at an oven set temperature of 500°C for an exposure time of 60 minutes, followed by electroplating a double layer coating consisting of an inner palladium (or nickel) layer and an outer gold layer, with a final diameter of 17.5 μm; Further drawing to a final palladium or nickel layer thickness ranging from 1 to 4 nm and a final gold layer thickness ranging from 10 to 18 nm followed by final strand annealing at an oven set temperature of 220° C. for an exposure time of 0.6 seconds, followed shortly thereafter by the obtained One coated wire was quenched in water containing 0.07 vol% surfactant.

Several different samples 1 to 12 of coated silver and silver-based wires and uncoated reference silver wires of 4N purity (Ref) were prepared through this procedure. Table 1 shows the composition of a wire with a diameter of 17.5 μm. Its composition was determined by ICP.

Table 2 below shows specific test results. All tests were performed using a wire with a diameter of 17.5 μm, except for the electron transfer test, which was performed using a wire with a diameter of 75 μm.

Claims (10)

A method of electrically connecting a contact surface of a first electronic component to a contact surface of a second electronic component, comprising:
(1) capillary wedge bonding a wire having a circular cross-section with an average diameter of 8 to 80 ㎛ to the contact surface of the first electronic component;
(2) lifting the capillary wedge bonded wire to form a wire loop between the capillary wedge bond formed in step (1) and the contact surface of the second electronic component; and
(3) stitch bonding the wire to the contact surface of the second electronic component
Includes,
The capillary wedge bonding in step (1) is performed using a ceramic capillary with a bottom angle in the range of 0 to 4 degrees,
The wire includes a wire core having a surface, the wire core having a double layer coating superimposed on the surface,
The wire core itself comprises a material selected from the group consisting of pure silver, doped silver with a silver content greater than 99.5 wt%, and silver alloys with a silver content of at least 89 wt%,
wherein the double layer coating consists of an inner layer of nickel or palladium from 1 to 50 nm thick and an adjacent outer layer of gold from 5 to 200 nm thick. According to paragraph 1,
Step (1) is performed using a KNS-iConn bonder, and the capillary wedge bonding process parameters are:
(a') ultrasonic energy ranging from 50 to 100 mA,
(b') force ranging from 10 to 30 g,
(c') constant velocity in the range of 0.3 to 0.7 μm/s,
(d') contact threshold ranging from 60 to 70%,
(e') a bonding temperature ranging from 25 to 175° C.,
(f') an extension of the tail length ranging from 200 to 500 μm, and
(g') ultrasonic lamp ranging from 0 to 50%
contains at least one of, or
Step (1) is performed using a Shinkawa bonder, and the capillary wedge bonding process parameters are:
(a") ultrasonic energy in the range of 50 to 100 mA,
(b") force ranging from 10 to 30 g,
(c") constant velocity in the range of 0.3 to 0.7 μm/s,
(d") contact threshold ranging from 60 to 70%;
(e") bonding temperature ranging from 25 to 175° C.,
(f") cut tail length ranging from 85 to 110 μm;
(g") a sink amount ranging from -6 to -12 μm, and
(h") Ultrasonic slope ranging from 0 to 50%
A method that includes at least one of the following. 3. The method of claim 1 or 2, wherein the wire core comprises pure silver comprising 99.95 to 100 wt% silver and up to 500 wtppm of additional non-silver components. 3. The wire core of claim 1 or 2, wherein the wire core contains greater than 99.5 to 99.997 wt% silver, 30 to less than 5000 wtppm of at least one doping element, and up to 500 wtppm of silver other than the at least one doping element. A method comprising doped silver comprising additional components. 3. The wire core of claim 1 or 2, wherein the wire core is doped with 89 to 99.50 wt% of silver, 0.50 to 11 wt% of at least one alloying element, and less than 5000 wtppm of at least one alloying element other than said at least one alloying element. elements, and a silver alloy comprising up to 500 wtppm of silver, additional components other than said at least one alloying element and said at least one doping element. 6. The method of claim 5, wherein the at least one alloying element is selected from the group consisting of palladium, gold, nickel, platinum, copper, rhodium, and ruthenium. 6. The method of claim 5, wherein the at least one doping element is selected from the group consisting of calcium, nickel, platinum, copper, rhodium, and ruthenium. The method of claim 1 or 2, wherein the first electronic component is a semiconductor having a contact surface in the form of a substrate having a contact surface or a bond pad, and the second electronic component is a substrate having a contact surface or a contact in the form of a bond pad. A method wherein the semiconductor has a surface. The method of claim 8, wherein the first electronic component is a semiconductor having a contact surface in the form of a bond pad, and the second electronic component is a substrate having a contact surface. The method of claim 8, wherein the first electronic component is a substrate having a contact surface, and the second electronic component is a semiconductor having a contact surface in the form of a bond pad.